See:
- http://archaeologyinbulgaria.com/2015/09/06/archaeologists-discover-saints-crypt-in-early-christian-basilica-in-roman-and-byzantine-fortress-zaldapa-in-northeast-bulgaria/
- http://archaeologyinbulgaria.com/2017/01/19/archaeologists-find-huge-crypt-with-early-christian-martyrs-bones-in-roman-byzantine-city-zaldapa-in-northeast-bulgaria/
- Efthymios Rizos, Centres of the late roman military supply network in the Balkans: a survey of horrea, In: Römisch-Germanisches Zentralmuseum: Jahrbuch des Römisch-Germanischen Zentralmuseums Mainz, Heidelberg 2013, pp. 659-696